1. Field of the Invention
The present invention relates to the field of plant molecular biology and plant genetic engineering, and polynucleic acid molecules useful for gene expression in plants. Specifically, the present invention discloses chimeric polynucleic acid molecules that function as promoters in plant cells. The invention further discloses DNA constructs, plant cells and plants comprising said polynucleic acid molecules, and methods of producing and using the same.
2. Description of Related Art
One of the goals of plant genetic engineering is to produce plants with agronomically desirable characteristics or traits. The proper expression of a desirable transgene in a transgenic plant is one way to achieve this goal. Elements having gene regulatory activity, i.e. regulatory elements such as promoters, leaders, introns and transcription termination regions, are non-coding polynucleotide molecules that play an integral part in the overall expression of genes in living cells. Regulatory elements that function in plants are therefore useful for modifying plant phenotypes through the methods of genetic engineering.
Many regulatory elements are available and are useful for providing good overall gene expression. For example, promoters such as the MAS promoter (U.S. Pat. No. 5,955,646), a ubiquitin promoter (U.S. Pat. Nos. 6,528,701; 6,638,766 ), P-FMV, the promoter from the 35S transcript of the Figwort mosaic virus (U.S. Pat. No. 6,051,753); P-CaMV 35S, the promoter from the 35S RNA transcript of the Cauliflower mosaic virus (U.S. Pat. No. 5,530,196); P-Os Act1, the promoter from the actin 1 gene of Oryza sativa (U.S. Pat. No. 5,641,876); and P-nos, the promoter from the nopaline synthase gene of Agrobacterium tumefaciens are known to provide gene expression in most or all of the tissues of a plant during most or all of the plant's lifespan. While previous work has provided a number of regulatory elements useful to affect gene expression in transgenic plants, there is still a great need for novel regulatory elements with beneficial expression characteristics. Many previously identified regulatory elements fail to provide the patterns or levels of expression required to fully realize the benefits of expression of selected genes in transgenic crop plants. One example of this is the need for regulatory elements capable of driving gene expression in different types of plant tissues, and either expressed constitutively but selectively in certain tissue or cell types, or during desirable stages of a plants cell or tissue growth and development.
A plant promoter is a key element for directing transgene expression in a plant cell or tissue. The transcription machinery is assembled and transcription is initiated from the promoter DNA molecule. Transcription factors influence the strength and temporal expression of a transcript from a promoter molecule. Accordingly, regions within the promoter molecule function to enhance or repress transcription.
The genetic enhancement of plants and seeds provides significant benefits to society. For example, plants and seeds may be enhanced with a transgene to provide desirable agricultural, biosynthetic, commercial, chemical, insecticidal, industrial, nutritional, or pharmaceutical properties. Despite the availability of many molecular tools, however, the genetic modification of plants and seeds is often constrained by an insufficient or poorly localized expression of the engineered transgene.
It is of immense social, ecological and economic interests to develop plants that have enhanced nutrition, improved resistance to pests, and tolerance to harsh conditions such as drought. Thus, the identification of new regulatory elements (e.g., promoters) that function in various types of plants is useful in developing enhanced varieties of crops. Clearly, there exists a need in the art for new promoter molecules that are capable of expressing heterologous nucleic acid molecules in important crop species. It is disclosed herein that chimeric promoter DNA molecules comprising a viral promoter DNA enhancer region and a promoter DNA region from a plant proline rich protein (Prp) gene provide an unexpected range of promoter strength and tissue enhanced expression in transgenic plants, and in some cases exhibits a pronounced ability to effectively deliver a pesticidal agent to a pest feeding on the transgenic plant, resulting in increased suppression of pest infestation of the transgenic plant compared to expression of the same pesticidal agent from the Prp promoter segment alone or in combination with other viral enhancer segments. These promoter molecules that exhibit constitutive, temporal, developmental, or tissue-specific expression patterns are of great interest in the development of plants that exhibit agronomically desirable traits.